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Introduction to Remote Service Calls Slides for CSCI 3171 Lectures E. W. Grundke

Introduction to Remote Service Calls Slides for CSCI 3171 Lectures E. W. Grundke. References. D. E. Comer Computer Networks and Internets, 3rd ed. (Chapter 35: RPC and Middleware) Prentice-Hall 2001 A. Tanenbaum and M. van Steen (TvS) Distributed Systems: Principles and Paradigms

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Introduction to Remote Service Calls Slides for CSCI 3171 Lectures E. W. Grundke

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  1. Introduction to Remote Service Calls Slides for CSCI 3171 Lectures E. W. Grundke

  2. References • D. E. Comer • Computer Networks and Internets, 3rd ed. • (Chapter 35: RPC and Middleware) • Prentice-Hall 2001 • A. Tanenbaum and M. van Steen (TvS) • Distributed Systems: Principles and Paradigms • Prentice-Hall 2002 • G. Coulouris, J. Dollimore and T. Kindberg (CDK) • Distributed System: Concepts and Design • Addison-Wesley 2001

  3. Acknowledgement • Some slides from: • TvS: http://www.prenhall.com/divisions/esm/app/author_tanenbaum/custom/dist_sys_1e/ • CDK: http://www.cdk3.net/ig/beida/index.html

  4. Remote Procedure Calls (RPC)

  5. Motivation • Writing clients and servers is error-prone (certainly in C!)(much low-level detail, yet common basic patterns) • Instead: - hide communications behind a “function call”- specify a high-level interface only- let an automated tool generate the actual client/server code • Advantage: • - Focus programmer attention on the application, not on the communications.- Familiar function-calling paradigm

  6. What is RPC? • Call a procedure (function, subroutine, method, …) • in a program • running on a remote machine, • while hiding communication details from the programmer. • Note: Think C, not java! We deal with objects later!

  7. Standards for RPC • RFC 1057: Remote Procedure Call • RFC 1014: External Data Representation • Author: Sun Microsystems Inc. • Others: see Comer. • Sun RPC Demo with the rpcgen tool: • http://www.eng.auburn.edu/department/cse/classes/cse605/examples/rpc/stevens/SUNrpc.html

  8. Conventional Procedure Call • Parameter passing in a local procedure call: the stack before the call to read • The stack while the called procedure is active TvS 2.7

  9. Conventional Parameter Passing Techniques • Call-by-value • Call-by-reference • Call-by-copy/restore

  10. Complications for Remote Calls • How to make it look like a function call, but actually use a client and server? • Answer: use “stubs” (“proxies”) • How to handle parameters and return values? • Platform differences (e.g. endian issues)Pass-by-reference • Answer: use “external data representation”

  11. Timing (Synchronous RPC) • RPC between a client and server program. TvS 2.8

  12. Steps of a Remote Procedure Call • Client procedure calls client stub in normal way • Client stub builds message, calls local OS • Client's OS sends message to remote OS • Remote OS gives message to server stub • Server stub unpacks parameters, calls server • Server does work, returns result to the stub • Server stub packs it in message, calls local OS • Server's OS sends message to client's OS • Client's OS gives message to client stub • Stub unpacks result, returns to client TvS 2.9

  13. Passing Value Parameters • Steps involved in doing remote computation through RPC 2-8 TvS 2.10

  14. Parameter Specification and Stub Generation • A procedure • The corresponding message. TvS 2.12

  15. Passing Reference Parameters • Reference variables (pointers):pointers to arrayspointers to structures (objects without methods) • What if the structure contains other pointers? • The server may need a whole “graph” of structures! • “Parameter marshalling”

  16. Asynchronous RPC • The interconnection between client and server in a traditional RPC • The interaction using asynchronous RPC 2-12 TvS 2.14

  17. Asynchronous RPC:Deferred Synchronous RPC • A client and server interacting through two asynchronous RPCs TvS 2.15

  18. External Data Representation

  19. Motivation • Data in running programs:Not just primitives, but arrays, pointers, lists, trees, etc. • In general: complex graphs of interconnected structures or objects • Data being transmitted: • Sequential! Pointers make no sense. Structures must be flattened. • All the heterogeneities must be masked! (endian, binary formats, etc.) CDK 4.3

  20. What is an External Data Representation? • “An agreed standard for the representation of data structures and primitive values.” • Internal to external: “marshalling” • External to internal: “unmarshalling” • Examples: Sun XDR • CORBA’s Common Data Representation (CDR)Java Object Serialization

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